Major depressive disorder (MDD) has a lifetime prevalence rate of approximately 20% in the United States and is the leading cause of non-fatal disease burden worldwide. MDD can be debilitating for all, but beginning in early adolescence, women are twice as likely to experience MDD relative to men. Moreover, as they age, they are at disproportionately high risk for developing several serious medical conditions that frequently co-occur with MDD and presage early mortality, such as hypertension, heart disease, certain cancers, neurodegeneration, and stroke. Understanding mechanisms that may underlie the initial development of depression, especially among women, is therefore of paramount public importance. To address this issue, I will elucidate neural, inflammatory, and genomic processes associated with risk for MDD in adolescence. Recent studies have shown that social stress engages a network of brain regions involved in processing physical and social threat. Social stress also up regulates components of the immune system involved in inflammation, which has been implicated in the pathophysiology of depression. To examine for the first time social stress-induced alterations in neural activity and connectivity, pro-inflammatory cytokine activity, and genome-wide transcriptional activity that are associated with risk for MDD, I will conduct a study in which 25 adolescent girls at high risk for MDD (i.e., no personal history of any affective Axis I disorder, but a positive maternal history of MDD) and 25 adolescent girls at low risk for MDD (i.e., no personal or maternal history of any Axis I disorder) will be exposed to a brief episode of social rejection while undergoing an fMRI scan. In addition, blood samples will be obtained at four time-points during the study to test for social stress-induced changes in (a) levels of the pro-inflammatory cytokines TNF-?, IL-1?, and IL-6, and (b) inflammatory gene expression, using microarray-based genome-wide transcriptional profiling. As such, this study will be the first to examine neural, inflammatory, and genomic responses to social stress that are associated with differential risk for depression (Aims 1 & 2). The study will also be the firstto examine relations between these different stress-related mechanisms in adolescent girls at high and low risk for MDD (Aim 3). Finally, the study will allow me to obtain mentored training in several areas that are critical for pursuing this line of research independently, including: neuroscience and neuroimaging methods, fMRI data analysis, and functional genomics. My goal as a clinical psychologist is to identify mechanisms that underlie the initial emergence of risk fo depression and related disorders in adolescence, which can in turn be modified to reduce the enormous disease burden that is associated with these conditions. This Mentored Clinical Scientist Development Award will enable me to pursue this goal by providing me with protected time to obtain state-of-the-art training at UCLA. This award will also allow me to conduct the firs multi-method, experimental fMRI study on neural, inflammatory, and genomic mechanisms underlying risk for depression in adolescence, which will in turn inform the development of novel strategies for reducing the mounting disease burden associated with depression and depression-related diseases.